1. Field of the Invention
The present invention relates to a fuel injection control apparatus for an internal combustion engine which apparatus is capable of suppressing or preventing fuel leakage from a fuel injector in the state where the engine is stopped and which can be implemented without incurring any appreciable increase in the cost as compared with existing apparatuses.
2. Description of Related Art
In general, in the internal combustion engine (hereinafter also referred to simply as the engine) for automobiles or motor vehicles, fuel is supplied to the engine from a fuel tank by way of a fuel pump and a fuel supply pipe to be thereby injected into engine cylinder(s) through a fuel injector.
In such fuel injection system as mentioned above, vaporization of the fuel within the fuel supply pipe has to be suppressed or prevented in order to ensure high restarting performance of the engine from the state where a high temperature prevails.
To this end, in the hitherto known or conventional fuel injection control apparatus for the engine, a check valve is provided at the side of a discharge port of the fuel pump so that a high fuel pressure can be held within the fuel supply pipe by preventing the residual fuel pressure within the fuel supply pipe from lowering in the engine stoppage state (i.e., in the state where the engine operation is stopped).
However, when the fuel pressure within the fuel supply pipe continues to be held at a high level in the engine stoppage state, there may arise such unwanted situation that the fuel leaks into the intake pipe of the engine from the fuel injector.
FIG. 5 of the accompanying drawings is a view for graphically illustrating change of the fuel pressure [MPa] within the fuel supply pipe as a function of time lapse [min] in the engine stoppage state, wherein curve (a) represents the fuel pressure change in the conventional apparatus.
As can be seen from the curve (a) shown in FIG. 5, the fuel pressure held at a high level just after the stoppage of the engine operation lowers to a level equivalent to the atmospheric pressure (=0.1 [MPa]) within about 60 minutes. In that case, the quantity of gasoline or fuel leakage will amount to ca. 20 mcc per fuel pipe line.
The fuel leakage mentioned above provides a cause for increasing the amount of unburnt hydrocarbon (harmful gas) contained in the exhaust gas discharged in the succeeding engine starting operation (i.e., engine restarting operation).
FIG. 6 of the accompanying drawings is a view for graphically illustrating change of the concentration [ppm] of total hydrocarbon (THC) as a function of time [sec] in the engine starting operation, wherein a curve (a) represents the change of the THC concentration in the conventional apparatus.
As can be seen from the curve (a) shown in FIG. 6, the discharge quantity of hydrocarbon (HC) in the engine starting operation is very large initially for a time of about one second. Furthermore, since the quantity of fuel leakage from the fuel injector can not be controlled, it provides a cause for dispersion or variance of the exhaust gas components in the engine starting operation.
Besides, the fuel leaked into the intake pipe will increase the volume of fuel vapor gases emanated from the motor vehicle. At this juncture, it should be added that the exhaust gas condition in the conventional apparatus is going beyond the permissible level in the light of the statutory exhaust gas regulations which have become more severe in recent years.
Under the circumstances, there have been proposed various fuel injection control apparatuses for the internal combustion engines which tackle with the problems mentioned above.
By way of example, in the fuel injection control apparatus disclosed in Japanese Unexamined Patent Application Publication No. 108943/1994 (JP-A-6-108943), the fuel leakage from the fuel injector is suppressed by lowering the fuel pressure within the fuel supply pipe by opening a bypass valve which allows the fuel to return to the fuel tank when the engine is stopped.
Further, in the fuel injection control apparatus disclosed in Japanese Unexamined Patent Application Publication No. 42109/1997 (JP-A-9-42109), the fuel temperature and the fuel pressure are detected for thereby controlling a bypass valve such that a desired fuel pressure can be established within the fuel supply pipe in dependence on the fuel temperature in an effort to prevent or suppress the fuel leakage from the fuel injector while enhancing the engine restarting performance in a high temperature engine state.
In the case of the first mentioned conventional apparatus (described in JP-A-6-108943), such arrangement is adopted that the fuel is fed to the fuel supply pipe from the fuel tank when the bypass valve is closed upon starting of the engine operation (i.e., upon closing of an ignition switch).
Thus, the conventional apparatus mentioned above suffers a problem that in case the bypass valve should get out of order, there may undesirably arise such situation that the fuel can not be fed to the engine upon starting of the engine operation. Besides, when the fuel temperature is high, the fuel will return to the fuel tank incurring thus degradation in the high-temperature engine restarting performance, to another disadvantage.
On the other hand, in the case of the second-mentioned conventional apparatus (described in JP-A-9-42109), it is required to additionally provide a fuel temperature sensor and a fuel pressure sensor, which means that the cost involved in the implementation of the apparatus increases, giving rise to another problem.
As is apparent from the foregoing, the conventional fuel injection control apparatus such as described in JP-A-6-108943 suffers problems that the fuel can not be fed out when the bypass valve gets out of order and that the engine restarting performance becomes degraded when the fuel temperature is high.
Besides, the conventional fuel injection control apparatus such as described in JP-A-9-42109 is disadvantageous in that the fuel temperature sensor and the fuel pressure sensor are additionally required, incurring increase of the cost.
In the light of the state of the art described above, it is an object of the present invention to provide a fuel injection control apparatus for an internal combustion engine which can solve the problems mentioned above and which is capable of preventing or suppressing positively the fuel leakage from the fuel injector in the engine stoppage state by controlling the bypass valve on the basis of an estimated fuel temperature while rendering it unnecessary to provide additional sensors such as the fuel temperature sensor and the fuel pressure sensor.
In view of the above and other objects which will become apparent as the description proceeds, there is provided according to a general aspect of the present invention a fuel injection control apparatus for an internal combustion engine, which apparatus includes various types of sensors for detecting operation states of an internal combustion engine, a fuel pump and a fuel supply pipe for supplying a fuel from a fuel tank to the internal combustion engine, a fuel injector for injecting the fuel into the engine, an engine stoppage detecting means for detecting a stopped state of the engine, a fuel temperature estimating means for estimating temperature of the fuel within the fuel supply pipe, and a fuel pressure lowering means for lowering the pressure of the fuel within the fuel supply pipe, wherein the fuel pressure lowering means is designed to lower the pressure of the fuel within the fuel supply pipe after the stoppage of operation of the engine in dependence on an estimated fuel temperature determined by the fuel temperature estimating means.
By virtue of the arrangement of the fuel injection control apparatus described above, the fuel leakage from the fuel injector can positively be prevented in the state where the engine operation is stopped.
In a preferred mode for carrying out the present invention, the various types of sensors may include an intake air temperature sensor for detecting the temperature of an intake air of the engine, and the fuel temperature estimating means may be so designed as to estimate the temperature of the fuel on the basis of the temperature of the intake air.
With the arrangement of the fuel injection control apparatus described above, the estimated fuel temperature can arithmetically be determined with high accuracy and reliability without need for providing any additional sensor advantageously from the standpoint of the cost.
In another preferred mode for carrying out the present invention, the fuel supply pipe may include a bypass valve capable of regulating the pressure of the fuel, and the fuel pressure lowering means may be so designed as to compare the estimated fuel temperature value with a predetermined value to thereby open the bypass valve over a predetermined time period when the estimated fuel temperature value is greater than the predetermined value inclusive.
Owing to the arrangement of the fuel injection control apparatus described above, the fuel leakage from the fuel injector can positively be prevented in the state where the engine is stopped.
In yet another preferred mode for carrying out the present invention, the predetermined value mentioned above may be so set that substantially no inconvenience can take place upon restarting of operation of the internal combustion engine from a high temperature state thereof.
With the arrangement described above, the fuel leakage from the fuel injector can positively be prevented without incurring any problem upon restarting of the engine from the high-temperature state thereof.
In still another preferred mode for carrying out the present invention, the fuel injection control apparatus for an internal combustion engine which is equipped with starter for starting operation of the engine may further include a starter control means for controlling driving operation of the starter, wherein the starter control means is so designed as to drive the starter upon lapse of a predetermined delay time since a time point at which operation of the fuel pump has been started upon engine starting operation in a state where the fuel pressure has been lowered by the fuel pressure lowering means.
With the arrangement of the fuel injection control apparatus described above, generation of fuel vapor upon fuel injection in the engine starting operation can be suppressed, to further advantage.
In a further preferred mode for carrying out the present invention, the delay time mentioned above may be set to a time required for the pressure of the fuel to increase sufficiently since the time point at which the operation of the engine has been started.
Owing to the arrangement of the fuel injection control apparatus described above, engine operation can be started upon initial fuel injection with high reliability.
The above and other objects, features and attendant advantages of the present invention will more easily be understood by reading the following description of the preferred embodiments thereof taken, only by way of example, in conjunction with the accompanying drawings.